Cowboys, caimans, and mud come together in the Pantanal, where modern pressures threaten the health of one of the world's largest wetlands.

Get a taste of what awaits you in print from this compelling excerpt.

The cowhands who make their living in the Pantanal wetland have an unparalleled lexicon for mud. Plain old mud is just lama—or barro or lodo—as it is anywhere else in Brazil. But here in the Pantanal, the bare mud where cattle gather around a gate has its own name: maiadô. And so does deeply hoof-pocked mud with sharp ridges between the pocks: That's brocotó. Even the season that gives rise to all this mud has its own Pantanal name. The cheia, they call it, the "full," when this whole grand wetland floods knee-deep—hip-deep, waist-deep—with water.

The mud that underlies Beatriz Rondon's ranch, the Santa Sofia, is high in clay, and though her land rolls out like a glorious tallgrass prairie in the dry season, it turns into a diabolical, hoof-sucking bog called brejo in the full. Dawn finds our horses postholing through it, withers deep in gray-brown water. There are no cattle in sight, only jabiru storks and wood storks and roseate spoonbills and snail kites and, idling at the water's surface among chartreuse grasses, the ubiquitous crocodilians called caimans. My mare stumbles over one but, unlike me, shows no alarm, and the caiman simply glides away with a sidelong stare.

It's a tendon-wrenching, arduous ride, and before the parrots are done squawking the morning news from their roosts in the palms, mare and I are streaming sweat and plastered in mud—a gluey gray slurry for which no one offers a name.

Midafternoon we rein up at an elevated ribbon of forest. A pungent stink rolls out to greet us, and two dozen vultures flap away at our approach. Our small party dismounts, and Beatriz (called Bia), her ranch foreman, Urbano Vilalba, two cowhands, a naturalist named Marion Marcondes, and I follow our noses into the gloom of the woods.

The carcass has been dragged 25 yards (23 meters) from where Urbano found it yesterday, his attention drawn by circling vultures while out here shifting cattle around. Now it lies half submerged at the edge of the bog, bloated, discolored, and twitching with maggots. Two days ago it was a regal, cream-colored, long-horned, half-ton, humpbacked zebu bull worth $400 at current beef prices. Today it's jaguar kill.

That a jaguar has dined on bull is not a particularly noteworthy event in the Pantanal. Typically vultures alert the rancher, the rancher calls in a professional jaguar hunter, the hunter tracks the cat with a pack of scarred hounds, shoots it, and leaves the carcass for scavengers. Even though jaguar hunting is illegal in Brazil, it's still common in this remote, largely unpeopled realm. As a jaguar hunter put it to me: "Who's to know?"

There will be no jaguar hunter this time. Bia has signed a contract with a nonprofit conservation group trying to preserve the threatened cats in the Pantanal. Naturalist Marion Marcondes has ridden out here to verify that a jaguar killed one of Bia's bulls. She'll file a report, and Bia will be reimbursed—"partially reimbursed," Bia notes dryly—for her loss. In return Bia will let the jaguar live.

"I adore jaguar hunting," says Bia, 64, whose grandfather staked an enormous land claim here in 1892. "And I can't stand outsiders telling me what to do. But we have to go forward. The Pantanal is changing under our feet. Like it or not, we Pantaneiros have to change too."